Advances in combined orthodontic and surgical treatment in the past decade have made it possible to correct or significantly improve dentofacial deformities which could not be treated previously. Although the long-term results of orthognathic surgery are stable in most instances, there are some post-treatmnt morphologic changes in almost all patients and significant relapse in a few. The alterations in jaw position and oral cavity volume produced by this surgery require considerable physiologic adaptation. It is likely that the extent of post-treatment morphologic change is related to the degree and pattern of physiologic adaptation. In this project, patients treated in the UNC Dentofacial Clinic will be studied. Morphologic stability will be evaluated and correlations will be sought between post-treatment morphologic changes and: (1) posture of head, mandible and tongue; (2) breathing pattern, as evaluated from nasal air flow and nasal resistance; (3) lip pressures; (4) vertically directed occlusal (biting) forces; and (5) vertically directed tongue forces. Elucidation of these relationships will provide insight into soft tissue function as a factor in the etiology of dentofacial deformity as well as a determinant of post-treatment stability.